Abstract

We investigate the spatial distribution of the light modulation that is produced by quantum-well excitons in an applied electric field. We study the field configuration in which the field is applied parallel to the quantum-well layers because this geometry is well-suited to high-speed traveling-wave modulation schemes.¹ In our experiments high-resistivity (semi-insulating) quantum wells are required to reduce ohmic dissipation and dielectric losses for terahertz electrical signals. We have measured the spatial distribution of the electroabsorption of quantum-well excitons by constructing a high-magnification infrared microscope in which the sample is uniformly illuminated with narrowband laser-diode light at the exciton wavelength.² We image the transmitted light onto an infrared charge-coupled-device camera and digitally subtract the image as we vary the bias voltage. We obtain a compete color-mapped difference image, which allows us to obtain the lateral depletion profile versus bias, polarity, etc.

© 1990 Optical Society of America